High-contrast, Reversible Change of Thermal Conductivity in Hexagonal Nickel-Iron Sulfides

Materials showing abrupt change of thermal conductivity are strongly desired for rapidly developing thermal regulation applications. Here, we report a sharp change of thermal conductivity (Δκ/κ0) up to 200% within a temperature interval of ~ 40 K in hexagonal sulfides Ni1-xFexS bonded with silver. Such Δκ/κ0 values exceed those reported in other thermal regulation materials, e.g., VO2 series (Δκ/κ0<100%). The large jump of thermal conductivity roots from the dramatic modification of the electronic structure at the first-order phase transition. Moreover, the addition of silver overcomes the inherent brittleness of Ni1-xFexS and thus improves machinability and thermal cycling stability, which is beneficial to the practical applications. Our work presents a new promising material for thermal management applications.